The structure near the terminal pole of a conventional closed secondary battery is shown in a sectional view in FIG. 2. In FIG. 2, a terminal pole 21 is disposed by penetrating a cover 22 of a closed secondary battery 20 from inside to outside of the battery. An annular packing 25 is fitted into an annular groove 24 formed in a disk-shaped flange 23 positioned inside of the battery of the terminal pole 21. By fitting in an annular spring 27 while pulling up a pole of this terminal hole 21 to the outside of the battery, the terminal pole 21 is fixed at a specified position as shown in FIG. 2. By the pulling action when fixing the terminal pole 21, the annular packing 25 placed in the annular groove 25 of the flange 23 is compressed between the flange 23 and the inner surface of the cover 22. A sealing agent such as asphalt pitch is applied around the packing 25, which enhances the effect of preventing electrolyte leak by the addition of this sealing agent. In such constitution, the passage of the leaking electrolyte from the gap between the cover 22 and terminal pole to the outside of the battery is shut off, so that electrolyte leak from inside of the battery can be prevented.
However, when the closed secondary battery 20 is used for a long time, the sealing agent deteriorates, and the effect of preventing the electrolyte leak of the battery declines, and the electrolyte contained in the closed secondary battery may escape outside.
The invention solves the problems of the prior art, and presents a closed secondary battery enhanced in the effect of preventing electrolyte leak.